Many RF antenna systems are required to receive signals over a wide field of view (FOV). Yet, if the angle of arrival in elevation and azimuth is unknown a priori then emissions may go undetected. Electronically scanned antenna arrays can provide receive beams across a FOV, but there is a cost and complexity to the processing and data transfer for each beam formed. Further, many RF systems can receive signals over a wide range of frequencies, but it is computationally expensive to detect signals over a wide range. Also, if the angular extent of beams are large, then there may be many signals received in each beam. To avoid interference of unwanted signals and maximize sensitivity, it is desirable to create each beam using all the elements in an array, creating one or more full aperture beams, which have the smallest angular extent (highest angular resolution) of any beam created by that array.
Filling the FOV of an array with high resolution, full aperture beams requires the received signal to be sampled at each element, and incurs a cost proportional to the number of elements receiving the signal and bandwidth of the received signal. Some narrowband systems form large numbers of high resolution beams using exceptional, brute force beamforming computers. Wideband systems, however, have either employed beams with little or no angular resolution, involving few elements, having relatively low sensitivity and a high susceptibility to interference, or small numbers of high resolution beams pointed at angles within the FOV (known to contain signals). Wideband digital antennas can generate significant amounts of data, e.g., on the order of 10-100 Gbit/sec per antenna element, requiring either extensive processing near the antenna elements or high power transport electronics for the data. To form a beam, data from the respective elements must be time delayed (typically requiring interpolation), so the data arriving from any specified angle adds coherently when the samples are combined. To reduce computational or transport complexity, the data can be filtered to a reduced bandwidth and or groups of elements may be combined before transport. Filtering or combining the data limits what can be detected in later processing, as combined elements (sub-arrays) receive signals from only a portion of the FOV.
Thus, what are needed are apparatus and methods for determining where in angle, and ideally where in frequency, signals are located so that full aperture beams can be formed at those angles and received data filtered to retain only portions of the spectrum where signals are located. Optimally, such systems would use the same equipment otherwise used in the array and could ideally fill a FOR with beams that can detect and locate the angle and frequency of incident signals, and cue full(er) sensitivity beams for interrogating detected signals for additional detail and characterization.